Abstract: Objective To determine the optimal dose of colloid preload, which is both safe and effective, for preventing
hypotension in parturients undergoing cesarean section under spinal anesthesia. Methods Forty-five healthy, termed
parturients scheduled for cesarean delivery under spinal anesthesia were randomly assigned to 3 colloid preload groups to
receive gelofusine infusion at the rates of 5, 10, or 15 ml·kg-1·h-1 (groups I, II, and III, respectively). Colloid preload was
administered 10 min before spinal anesthesia and maintained until the delivery. Blood pressure (BP) and heart rate (HR) of the
parturients were monitored during the operation, and Apgar scores at 1 and 5 min after birth were recorded. S100β protein
concentration and blood gas values of the umbilical artery were also measured. The vascular adaptation in the placental villous
capillary was evaluated stereologically. Results At each time point of measurement, BP and HR showed no significant
differences among the 3 groups during the operation (P>0.05), but within the same group, BP and HR underwent significant
variations during the operation; groups II and III maintained more stable hemodynamics compared to group I. Apgar scores
and blood gas analysis, pH value, and S100β protein in the umbilical artery showed no significant differences among the 3
groups (P>0.05). The 3 groups exhibited no significant differences in the length and volume density of the placental villous
capillaries (P>0.05). Conclusion Colloid preload with gelofusine administered at the rate of 10 ml·kg-1·h-1 can reduce the
incidence and severity of hypotension in cesarean section under spinal anesthesia with the least adverse maternal and fetal
effects.